Production of sound records



June 20,1944. sTEUBE 2,352,032

PRODUCTION OF OOUND RECORDS Filed Feb. 17, 1942 flu/en for FF/TZ STEl/BE fliiorneg.

Patented June 20, 1944 PRODUCTION 01' SOUND RECORDS Fritz Steube, Leipzig, Germany: vested in the Allen Property Custodian Application February 17, 1942, Serial No. 431,266 In Germany August 12, 1940 3 Claims.

My present invention relates to the production of sound records and more particularly to a method in which a negative film having an especial blackening curve is used.

In accordance with my invention there is used a negative emulsion having a biackening'curve so constructed that a straight copy transparency curve starting from a transparency value below 2% and ending with a value of about 80% is obtained with the usual blackening curve of the positive film. In the production of sound films according to the varying density recording system and preferably in the production of sound records free from background noises (unmodulated frequency transparency distortion) it is especially important that there is a straight transparency curve as long as possible which also takes a fully linear course with low transparency values. This requirement must be fulfilled at all events in normally recording free from background noises as well as in recording according to the push-pull- B-method and the track-limiting-method.

The invention will be better understood from the following description when considered in connection with the accompanying drawing. Referring thereto Figure 1 shows a positive and a negative blackening curve, Figure 2 a transparency curve, and Figure 3 three different negative blackening curves.

For the production of varying density records the straight line method or the toe-inethod have hitherto been used. In the straight line method (the blackening curve of the negative film is represented by the curve a, Figure 3) there are utilized the straight parts of the negative and positive blackening curves which must satisfy the requirement of yielding the gamma-product 1. In this case the copy transparency curve starts from very low transparency values but ends already relatively early at a value of about 20% that is approximately the point X where in Figure 1 the straight part of the positive blackening curve begins. The straight line method is conveniently used for methods free from background 'noises. However, it is of disadvantage inasmuch as only a relatively small sound volume is attained in the reproduction. The toe"-method (the negative blackening curve is designated by b in Fi ure 3) which depends in the negative as well as in the positive upon the bowed lower parts of the blackening curve overcomes this drawback. In Figure 1 the positive blackening curve is utilized approximately from to X. The resulting minimum unmodulated frequency transparency,

however, is relatively great so that a satisfactory "noiseless eflect cannot be obtained.

In using normal positive film it has hitherto not been possible to combine both methods mentioned above in such a manner that the advantages oi! the two recording systems are also maintained as far as possible. This combination is made possible in accordance with the present invention by using an especially constructed negative blackening curve of the type as designated by c in Figure 3.

Figure 1 shows the normal positive blackening curve and the negative blackening curve which in connection with the former curve yields the copy transparency curve as represented in Figure 2. The negative blackening. curve is rectilinear with low densities. The gamma-value thereof is the reciprocal of the positive gamma in the rectilinear portion. With higher densities about from S=0.8

- the negative blackening curve is characterized by a gradual increase of the gamma-value. The course of the curve, however, may then again be rectilinear in the range of high densities.

In order more fully to illustrate the correlations between the Figures 1 and 2 three certain points X, and O are representedtherein. In Figure 1 the values there of are moreover given numerically. The point 0 of the negative curve corresponds with a light amount of i.t-=59 (Figure 2) .log it then is 1.77. By this illumination the blackening 1.9 or the transparency 1.26% is obtained on the negative. If the light amount Ltp of a copying light passing through the abovementioned blackening of the negative is 1.26 and log tip is 0.1 (Figure 1, point 0 of the positive curve), the corresponding blackening is 0.03, i. e. T=93%. This value has been plotted in Figure 2 as the ordinate for O. In an analogous manner the points and X of Figures 1 and 2 have been determined.

A negative emulsion which fulfils these conditions may be obtained by mixing at least one flatly graduated high-sensitive iemulsi'on with at least one steeply graduated less sensitive emulsion in an appropriate proportion or casting the emulsions to form at least two layers. In this latter combination in which the "mixing proportion" may, for instance, be adjusted by controlling the thickness of the layers it is possible to sensitize one or both above mentioned types of emulsion in the same or different colors and to adjust the gradation curve as completely as possible to that of the positive emulsion while suitably varying the color of the light during exposure. Moreover, screen dyes and other substances usual in the production of photographic layers may be added to one or both emulsions.

The advantages which are reached in using such negative curves are great. As the most important advantage there is to be mentioned the great dynamics which can chiefly be obtained it is essentially lower than that of the toev method.

Besides the above mentioned improvements of the recording according to the noiseless varying density recording system combined with unmodulated frequency transparency distortion and according to the B-varying density recording system there are further advantages of the negative emulsion in question in using the track limiting varying density recording system. Due to the greater sound volume the varying density has hitherto been recorded subsequently to the toe-method. For this method there are necessary comparatively low copying light intensities which, however, cannot sufficiently blacken the lateral cover portions. Owing to the negative emulsion of the present invention this drawback is avoided by using as the toe the transi tion region between the flat and the steep portions of the blackening curve. It is understood that the fiat straight region of the curve is conveniently utilized additionally. i

The above description and examples are intended to be illustrative only. I therefore do not intend to be limited in the patent granted except as required by the prior art and the appended claims.

I claim:

1. In a method of producing sound records, the improvement which comprises photographically recording sound upon a light-sensitive negative film adapted to the normal positive film serving as the copying material, said negative film comprising at least two negative emulsions yielding a characteristic negative blackening curve, said curve being rectilinear to the black ening of about 0.8 and subsequently passing into a non-linear gradually rising curve, the gammavalue 01 the rectilinear portion of said negative curve corresponding with the reciprocal of the steepness in the rectilinear portion of the positive blackening curve, and copying the track thus obtained onto a film comprising a normally graduated positive emulsion to produce a transparency curve rectilinear throughout the whole blackening region.

In a method of producing sound records, the improvement which comprises photographically recording sound upon a light-sensitive negative film adapted to the normal positive film serving as the copying material, said negative film comprising a mixture of at least two negative emulsions yielding a characteristic negative blackening curve, said curve being rectilinear to the blackening of about 0.8 and subsequently passing into a non-linear gradually rising curve, the gamma-value of the rectilinear portion of said negative curve corresponding with the reciprocal of th steepness in the rectilinear portion of the positive blackening curve, and copying the track thus obtained onto a film comprising a normally graduated positive emulsion to produce a transparency curve rectilinear throughout the whole blackening region.

3. In a method of producing sound records, the improvement which comprises photographically recording sound upon a light-sensitive negative film adapted to the normal positive film serving as the copying material, said negative film comprising at least two negative emulsions cast upon one another and yielding a characteristic negative blackening curve, said curve being rectilinear to the blackening of about 0.8 and subsequently passing into a non-linear gradually rising curve, the gamma-value of the rectilinear portion of said negative curve corresponding with the reciprocal of the steepness in the rectilinear portion of the positive blackening curve, and copying the track thus obtained onto a film comprising a normally graduated positive emulsion to produce a transparency curve rectilinear throughout the whole blackening region.

FRITZ STEUBE. 

